7. Electronics design

Assignments and Assessment

Group assignment:
Use the test equipment in your lab to observe the operation of a microcontroller circuit board (as a minimum, you should demonstrate the use of a multimeter and oscilloscope)
Document your work on the group work page and reflect what you learned on your individual page

Individual assignment:
Use an EDA tool to design a development board that uses parts from the inventory to interact and communicate with an embedded microcontroller

Learning outcomes
- Select and use software for circuit board design
- Demonstrate workflows used in circuit board design

Have you answered these questions?
- Linked to the group assignment page
- Documented what you have learned in electronics design
- Checked your board can be fabricated
- Explained problems and how you fixed them.
- Included original design files (Eagle, KiCad, etc.)
- Included a hero shot

Terminologies and its desriptions

Components

• Ribbon Cable - A flat, multi-wire cable used for making multiple connections simultaneously, commonly used in data and signal transmission.
• IDC Connector- (Insulation Displacement Connector) Designed to attach directly to ribbon cables without the need for soldering, making it easy to connect multiple wires at once.
• Button - A simple mechanical switch that momentarily connects or disconnects a circuit when pressed, often used for user inputs.
• Switch - A device that controls the flow of electricity by opening or closing a circuit. It can be toggle-based (on/off) or momentary like a push button.
• Resistor - A passive component that limits electrical current in a circuit, following Ohm’s Law (I = V/R). Different resistance values are used to regulate voltage and current in various applications.
• Capacitor - A component that stores and releases electrical energy, playing a key role in filtering, power supply stabilization, and signal processing.
  • Formulae: C = Q/V, I = C dV/dt
  • Unpolarized- Can be connected in any orientation, used in AC circuits.
  • Polarized - Electrolytic capacitors with marked polarity, commonly used in power supply circuits.
• Crystal / Resonator - Used for generating stable clock signals in microcontrollers and other timing applications, ensuring precise operation.
• Inductor - A coil of wire that stores energy in a magnetic field, commonly used in filters, transformers, and power electronics.
  • Formula: V = L dI/dt (Voltage across an inductor is proportional to the rate of change of current).
• Diode - A semiconductor device that allows current to flow in only one direction, protecting circuits from reverse voltage.
  • PN Junction Diode - Standard rectifier for converting AC to DC.
  • Schottky Diode - Fast-switching, low forward voltage drop, used in power applications.
  • Z- ener Diode - Allows reverse conduction at a specific voltage, used for voltage regulation.
  • LED (Light-Emitting Diode) - Converts electrical energy into light, widely used for indicators and displays.
• Transistor - A semiconductor device used as a switch or amplifier.
  • Bipolar Junction Transistor (BJT) - A current-controlled device with three terminals: collector, emitter, and base, used for amplification and switching.
  • MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) - A voltage-controlled device with three terminals: source, drain, and gate, used in power electronics and digital circuits.
• Battery, Regulator, DC-DC Converter - Power sources and voltage regulators that supply stable voltage levels to electronic circuits.
• Op-Amp (Operational Amplifier) - A high-gain voltage amplifier used in analog circuits for signal amplification, filtering, and mathematical operations.
  • Key functions: Differential amplifier, negative feedback, voltage gain, buffer (follower), transimpedance, transconductance.
• Microcontroller (MCU) - A small computer on a single chip with integrated peripherals like GPIO (General Purpose Input/Output), I2C, SPI, ADC (Analog-to-Digital Converter), and PWM. Used in embedded systems, automation, and control applications.
• Sensors - Devices that detect physical parameters such as temperature, light, pressure, motion, or proximity, converting them into electrical signals.
• Actuators - Components that convert electrical signals into mechanical movement, such as motors, solenoids, and relays.

Circuits

• Current (A) & Voltage (V)-
  • Electrical flow is often compared to water in pipes:
    • Current (A) - The amount of electrons flowing through a wire, similar to the volume of water flowing in a pipe.
    • Voltage (V) - The electrical potential difference, similar to water pressure.
  • Power is calculated using: P = I²R = IV (Power = Current² x Resistance = Voltage x Current).
• Kirchhoff’s Laws -
  • Kirchhoff’s Current Law (KCL) - The sum of currents entering a node equals the sum of currents leaving it.
  • Kirchhoff’s Voltage Law (KVL) - The total voltage around a closed loop equals zero, meaning energy is conserved.
• EDA (Electronic Design Automation) - The process of designing PCBs (Printed Circuit Boards) using specialized software.
  • Steps: Sketching, schematic design, component (auto)placement, (auto)routing, simulation, and fabrication.
  • Design Elements:
    • Layers – Multiple copper layers for signal routing.
    • Angles – Proper routing angles to minimize signal interference.
    • Vias – Holes connecting different PCB layers.
    • Power Planes & Ground Pours – Large copper areas for efficient power and ground distribution.

Test Equipment

• Regulated Power Supply - Provides adjustable voltage and current with protection features, ensuring stable power for circuit testing.
• Multimeter - A handheld tool for measuring voltage, current, and resistance, essential for troubleshooting circuits.
• Oscilloscope - Displays electrical signals in a time-dependent manner, helping analyze waveforms, frequencies, and signal integrity.
• Logic Analyzer - Captures and analyzes digital signals in microcontrollers, FPGAs, and communication protocols like SPI, I2C, and UART.
• Mixed Signal Analyzer- Combines oscilloscope and logic analyzer functions for debugging both analog and digital signals.
• Multichannel Analyzer - Used for observing multiple signals simultaneously, essential for complex systems.

Design Rules – according to docs.kicad.org

When designing a PCB, it’s essential to define proper design rules, especially when using specific milling tools. Since I use a 0.4mm end mill bit for cutting traces and a 0.8mm end mill bit for the board outline, I make sure to leave enough clearance between traces, pads, and the board edge to ensure clean milling and prevent unintended shorts.

Setting Up Design Rules in KiCad

• Access the Board Setup:
  • Open File > Board Setup… to configure the PCB layout parameters.
• Configure Constraints
  • Under Design Rules > Constraints, I define critical design parameters like minimum track width, clearance, and via sizes.
  • For my setup:
    • Clearance: I set the minimum clearance to at least 0.4mm to match the smallest milling bit size.
    • Edge Clearance: Ensuring at least 0.4mm distance between traces and the board outline prevents the 0.8mm milling bit from cutting into copper traces.
• Define Net Classes
  • Under Design Rules > Net Classes, I assign different clearance and width settings based on signal requirements.
  • Power traces often require wider tracks to handle higher currents, while signal traces can be narrower.

Verifying Design with Design Rule Checker (DRC)

After setting up the design rules and completing the PCB layout, I always verify my design to ensure it follows the constraints.

• Run the DRC
  • Open Inspect > Design Rules Checker and run a full check.
• Configure DRC Settings
  • Enable options like:
    • Refill all zones before performing DRC – Ensures copper zones are properly updated.
    • Report all errors for each track – Helps in pinpointing clearance issues.
• Review Violations
• If any violations are detected, they are listed in the DRC results. Clicking on them highlights the problematic areas, making it easy to correct the design.

By carefully setting up these rules and running the DRC before manufacturing, I ensure that my PCBs are error-free, easy to mill, and optimized for reliable performance.

Fab Electronics Library Installation for KiCad

I use KiCad 8 for my electronic design work, ensuring compatibility with the latest libraries and tools, as maintaining updates is crucial for efficiency. Since the library is constantly evolving, I recomend to pull the latest version before starting a project to avoid inconsistencies.

Installation of KiCad 8 and integration of Fab Libriaries to it

:memo: fab Installation instruction

• Clone or download this repository. You should rename the directory to fab.
• Store it in a safe place such as ~/kicad/libraries or C:/kicad/libraries.
• Run KiCad or open a KiCad .pro file.
• Go to “Preferences / Configure Paths” and add new environment variable “FAB” that points to location of the fab library on your drive, e.g. ~/kicad/libraries/fab. This is needed for the 3D models to load correctly.
• Go to “Preferences / Manage Symbol Libraries” and add fab.kicad_sym as symbol library.
• Go to “Preferences / Manage Footprint Libraries” and add fab.pretty as footprint library. KiCad Library Utils

Useful tutorials: Here, I watched clip from Adrian Torres which gives a brief and simple tutorial on creating a PCB board design in KiCAD 7.0, specifically with an ATTiny412 microcontroller to attempt to learn PCB board designing .

Design on ATtiny412_SSFR

1. Understanding the Basics of Schematic Design My learning journey began with understanding how to design a basic schematic using KiCad. I followed a tutorial to create a simple ATtiny412 circuit, which includes:

A microcontroller (ATtiny412) A 3-pin UPDI programming header A power decoupling capacitor (C1) An LED indicator with a current-limiting resistor (R1, 1kΩ) While creating the schematic, I learned about:

✅ Proper power (VCC) and ground (GND) connections
✅ Assigning functional pins like UPDI, TXD, and RXD
✅ Labeling signals and ensuring clear wiring

I also realized the importance of a pull-up resistor on UPDI for stable programming, which I initially overlooked.

1. Translating the Schematic to a PCB Layout After finalizing the schematic, I moved on to the PCB layout phase. This step involved:

Placing components efficiently to minimize trace lengths Routing connections to ensure proper electrical functionality Ensuring proper clearance and alignment for manufacturability Through multiple iterations, I observed:

✅ The importance of compact layout design for efficiency
✅ The need to adjust silkscreen labels for readability
✅ How trace widths affect power delivery and signal integrity

I also had to troubleshoot unrouted airwires, ensuring all required connections were complete.

1. Optimizing the PCB Design As I refined my PCB layout, I learned several best practices:

Using a ground plane instead of individual GND traces for better noise reduction Avoiding overlapping silkscreen text for clearer labeling Optimizing pad spacing to prevent soldering issues After implementing these improvements, I generated the 3D PCB model to visualize the final design.

1. Key Takeaways and Challenges 🚀 What I Achieved:

   ✔️ Successfully designed a working ATtiny412-based PCB ✔️ Learned schematic design, component placement, and PCB routing ✔️ Understood the importance of signal integrity and power management

Challenges Faced:

Initial routing mistakes that led to missing connections Component misalignment that needed fixing Refining silkscreen text placement for readability Overall, this learning experience gave me a strong foundation in PCB design, and I now feel more confident in creating custom circuit boards! I created the PCB board schematic shown below: